The broad goal of this project, Origins of Communication Disorders in Infants with Focal Brain Injury (FL), is to increase our understanding of the behavioral and neural mechanisms that underlie language development and language disorders from 0 - 6 years of age, with a particular emphasis on the cognitive, affective and neural factors associated with initial delays in language, and subsequent recovery from those delays, in children with unilateral injuries sustained before 6 months of age (i.e. prior to the onset of meaningful speech). Our research to date has demonstrated that early focal brain injury does result in specific and persistent deficits in linguistic and cognitive functioning, consistent with a growing both of evidence showing that the brain is not equipotential for all functions, even in the very early stages. However, these patterns do not map precisely onto the patterns of deficit and/or the correlations with lesion type observed in adults with comparable injury. Early deficits are less severe, the association between behavior and lesion type is more variable, and normal levels of functioning are eventually achieved in many cases. this recovery is particularly striking in language comprehension and production, suggesting that plasticity plays a significant role in brain organization for language. In a sample of 27 FL infants between 10 and 36 months of age (the largest sample in this age range that has ever been assembled and studied longitudinally), we have found significant delays in expressive vocabulary and early grammar. The initial delays (12 - 16 months) appear to be independent of size, side or intrahemispheric site of lesion. However, longitudinal and cross-sectional trends suggest that delays are more persistent in infants with lesions that involve left posterior cortex, consistent with the hypothesis that these injuries require a more extensive form of reorganization. Our cross-sectional work with a small sample of school age children with early FL provides a very different picture: all of the older children studied to date are functioning at normal or near-normal or near-normal levels in language comprehension and production, including subtle measures of discourse and grammar. Hence we have uncovered a possible "window of recovery" between 1 - 5 years of age, a critical phase in which children with early focal brain injury find alternative ways to solve the problem of language acquisition. We are now in a position to follow our prospective longitudinal sample through this window of recovery. We outline a specific set of hypotheses organized into three levels, corresponding to the theoretical goals of the Program Project as a whole: (1) identification of specific deficits in one or more areas of language, as a function of developmental level and lesion type, with a special focus on trajectories of recovery; (2) comparisons between language and other cognitive domains (especially spatial cognition) in the patterns of deficit and recovery that are observed, relevant to the issue of linguistic autonomy; (3) comparisons between FL children and the other populations under study in the Program Project, to uncover similarities and differences in the principles that govern early language deficits and subsequent recovery from those deficits.